1. Field of the Invention
The present invention relates to an IP telephone apparatus, an ENUM server, an IP telephone system, and a method for deleting terminal information. The present invention particularly relates to an IP telephone apparatus, an ENUM server and an IP telephone system that delete a NAPTR resource record from the ENUM server, and to a method for deleting a NAPTR resource record from the ENUM server.
2. Description of Related Art
Recently the Internet has been rapidly popularized. An IP telephone system has become the center of attention since a long distance communication can be performed at lower cost by using IP telephone apparatuses and since the IP telephone system enables users who have applied for the IP telephone system to communicate with each other through IP telephone apparatuses for free of charge. Additionally, an “ENUM (Telephone Number Mapping)” protocol is acknowledged as a protocol that associates the services using the Internet with the telephone numbers or associates the resources on the Internet with the telephone numbers. This ENUM protocol is specified in RFC2916 (Publication 1), which is being studied at the IETF (Internet Engineering Task Force) and the ITU-T (International Telecommunication Union-Telecommunication Standardization Sector).
The “ENUM” protocol has a function that converts a telephone number into a number corresponding to the E.164 system specified by the ITU-T and searches an IP address or a URI (Uniform Resource Identifier) using the mechanism of the DNS (Domain Name System) based on the converted telephone number.
An ENUM system is also being studied so that a service is provided using the “ENUM” protocol. In this ENUM system, an end user of the IP terminal apparatus such as, for example, an IP telephone apparatus which uses the ENUM system can select various functions (URI, the services using the URI {including telephone communication, e-mail and access to the database}). The end user, thus, needs to set the selected function into a “NAPTR (the Naming Authority Pointer)” resource record and to store the set NAPTR resource record in the ENUM system.
Additionally, the end user needs to instruct the ENUM server to transmit a request for the deletion when the registered NAPTR resource record is deleted.                [Publication 1] “ENUM Trial Japan First Report” ENUM Trial Japan, May 2004        
However, the end user of the conventional IP terminal apparatus such as an IP telephone apparatus using the “ENUM” protocol was required to instruct the ENUM server to transmit a request for the deletion when the NAPTR resource record was deleted. It was problematic in that the operation of deleting the NAPTR resource record became complex for the end users since the end users themselves had to transmit the request for the deletion.